Document EP1700964 shows a modular building system and a method for level assembling of prefabricated building modules. The modular system consists of high-resistance reinforced concrete module, to be stacked vertically and placed side-by-side in the construction of preferably residential buildings. Each module forms a monolithic structure or consists of a steel frame and panels with walls, roof and floor. These modules include positioning devices for stacking purposes; side connection elements between the modules and/or horizontal and vertical tightening bands. The modules are leveled by using leveling sheets and/or non-retraction mortar and/or a method with jacks and tubular sections filled with non-retraction mortar until it sets and the jacks are removed. Each building module includes all the accessories and finishing elements of a home, such as façades, windows, utilities, furniture and interior equipment.